linux/arch/x86/lib/memmove_64.S
Ingo Molnar 131484c8da x86/debug: Remove perpetually broken, unmaintainable dwarf annotations
So the dwarf2 annotations in low level assembly code have
become an increasing hindrance: unreadable, messy macros
mixed into some of the most security sensitive code paths
of the Linux kernel.

These debug info annotations don't even buy the upstream
kernel anything: dwarf driven stack unwinding has caused
problems in the past so it's out of tree, and the upstream
kernel only uses the much more robust framepointers based
stack unwinding method.

In addition to that there's a steady, slow bitrot going
on with these annotations, requiring frequent fixups.
There's no tooling and no functionality upstream that
keeps it correct.

So burn down the sick forest, allowing new, healthier growth:

   27 files changed, 350 insertions(+), 1101 deletions(-)

Someone who has the willingness and time to do this
properly can attempt to reintroduce dwarf debuginfo in x86
assembly code plus dwarf unwinding from first principles,
with the following conditions:

 - it should be maximally readable, and maximally low-key to
   'ordinary' code reading and maintenance.

 - find a build time method to insert dwarf annotations
   automatically in the most common cases, for pop/push
   instructions that manipulate the stack pointer. This could
   be done for example via a preprocessing step that just
   looks for common patterns - plus special annotations for
   the few cases where we want to depart from the default.
   We have hundreds of CFI annotations, so automating most of
   that makes sense.

 - it should come with build tooling checks that ensure that
   CFI annotations are sensible. We've seen such efforts from
   the framepointer side, and there's no reason it couldn't be
   done on the dwarf side.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-06-02 07:57:48 +02:00

210 lines
3.4 KiB
ArmAsm

/*
* Normally compiler builtins are used, but sometimes the compiler calls out
* of line code. Based on asm-i386/string.h.
*
* This assembly file is re-written from memmove_64.c file.
* - Copyright 2011 Fenghua Yu <fenghua.yu@intel.com>
*/
#include <linux/linkage.h>
#include <asm/cpufeature.h>
#include <asm/alternative-asm.h>
#undef memmove
/*
* Implement memmove(). This can handle overlap between src and dst.
*
* Input:
* rdi: dest
* rsi: src
* rdx: count
*
* Output:
* rax: dest
*/
.weak memmove
ENTRY(memmove)
ENTRY(__memmove)
/* Handle more 32 bytes in loop */
mov %rdi, %rax
cmp $0x20, %rdx
jb 1f
/* Decide forward/backward copy mode */
cmp %rdi, %rsi
jge .Lmemmove_begin_forward
mov %rsi, %r8
add %rdx, %r8
cmp %rdi, %r8
jg 2f
.Lmemmove_begin_forward:
ALTERNATIVE "", "movq %rdx, %rcx; rep movsb; retq", X86_FEATURE_ERMS
/*
* movsq instruction have many startup latency
* so we handle small size by general register.
*/
cmp $680, %rdx
jb 3f
/*
* movsq instruction is only good for aligned case.
*/
cmpb %dil, %sil
je 4f
3:
sub $0x20, %rdx
/*
* We gobble 32 bytes forward in each loop.
*/
5:
sub $0x20, %rdx
movq 0*8(%rsi), %r11
movq 1*8(%rsi), %r10
movq 2*8(%rsi), %r9
movq 3*8(%rsi), %r8
leaq 4*8(%rsi), %rsi
movq %r11, 0*8(%rdi)
movq %r10, 1*8(%rdi)
movq %r9, 2*8(%rdi)
movq %r8, 3*8(%rdi)
leaq 4*8(%rdi), %rdi
jae 5b
addq $0x20, %rdx
jmp 1f
/*
* Handle data forward by movsq.
*/
.p2align 4
4:
movq %rdx, %rcx
movq -8(%rsi, %rdx), %r11
lea -8(%rdi, %rdx), %r10
shrq $3, %rcx
rep movsq
movq %r11, (%r10)
jmp 13f
.Lmemmove_end_forward:
/*
* Handle data backward by movsq.
*/
.p2align 4
7:
movq %rdx, %rcx
movq (%rsi), %r11
movq %rdi, %r10
leaq -8(%rsi, %rdx), %rsi
leaq -8(%rdi, %rdx), %rdi
shrq $3, %rcx
std
rep movsq
cld
movq %r11, (%r10)
jmp 13f
/*
* Start to prepare for backward copy.
*/
.p2align 4
2:
cmp $680, %rdx
jb 6f
cmp %dil, %sil
je 7b
6:
/*
* Calculate copy position to tail.
*/
addq %rdx, %rsi
addq %rdx, %rdi
subq $0x20, %rdx
/*
* We gobble 32 bytes backward in each loop.
*/
8:
subq $0x20, %rdx
movq -1*8(%rsi), %r11
movq -2*8(%rsi), %r10
movq -3*8(%rsi), %r9
movq -4*8(%rsi), %r8
leaq -4*8(%rsi), %rsi
movq %r11, -1*8(%rdi)
movq %r10, -2*8(%rdi)
movq %r9, -3*8(%rdi)
movq %r8, -4*8(%rdi)
leaq -4*8(%rdi), %rdi
jae 8b
/*
* Calculate copy position to head.
*/
addq $0x20, %rdx
subq %rdx, %rsi
subq %rdx, %rdi
1:
cmpq $16, %rdx
jb 9f
/*
* Move data from 16 bytes to 31 bytes.
*/
movq 0*8(%rsi), %r11
movq 1*8(%rsi), %r10
movq -2*8(%rsi, %rdx), %r9
movq -1*8(%rsi, %rdx), %r8
movq %r11, 0*8(%rdi)
movq %r10, 1*8(%rdi)
movq %r9, -2*8(%rdi, %rdx)
movq %r8, -1*8(%rdi, %rdx)
jmp 13f
.p2align 4
9:
cmpq $8, %rdx
jb 10f
/*
* Move data from 8 bytes to 15 bytes.
*/
movq 0*8(%rsi), %r11
movq -1*8(%rsi, %rdx), %r10
movq %r11, 0*8(%rdi)
movq %r10, -1*8(%rdi, %rdx)
jmp 13f
10:
cmpq $4, %rdx
jb 11f
/*
* Move data from 4 bytes to 7 bytes.
*/
movl (%rsi), %r11d
movl -4(%rsi, %rdx), %r10d
movl %r11d, (%rdi)
movl %r10d, -4(%rdi, %rdx)
jmp 13f
11:
cmp $2, %rdx
jb 12f
/*
* Move data from 2 bytes to 3 bytes.
*/
movw (%rsi), %r11w
movw -2(%rsi, %rdx), %r10w
movw %r11w, (%rdi)
movw %r10w, -2(%rdi, %rdx)
jmp 13f
12:
cmp $1, %rdx
jb 13f
/*
* Move data for 1 byte.
*/
movb (%rsi), %r11b
movb %r11b, (%rdi)
13:
retq
ENDPROC(__memmove)
ENDPROC(memmove)